Generally, financial devices are devices that automatically process financial business desired by customers. The financial devices may deposit or withdrawal a medium (for example, bills, checks, certificates, etc) or transfer a medium.
Such a financial device may comprise a medium image detection apparatus. The medium image detection apparatus may detect a magnetic strip, images, a silver strip, fluorescent ink, various figures, various charters which are printed on a medium to determine a kind of medium, whether the medium is forged, and whether the medium is normal.
The medium image detection apparatus comprises an image sensor. The image sensor obtains image data of a medium. However, in the medium image detection apparatus according to the related art, an image obtained by the image sensor is changed in brightness by the external conditions such as a variation in transferring speed of the medium or an increase in ambient temperature due to heat generated by a motor. Thus, there is a limitation that a medium using the image obtained by the image sensor is deteriorated in recognition performance.